Vitamin A (Retinoids)

Preview this chapter:

Vitamin A (Retinoids), Page 1 of 1

< Previous page | Next page > /docserver/preview/fulltext/9781681088921/chapter-11-1.gif

The name of vitamin A designates the group of retinoids, i.e., some lipophilic substances, which include carotenoids, retinol, retinal and retinoic acid and their synthetic derivatives. Carotenoids and retinoids have several similar biological activities such as antioxidant properties, beneficial effects on the skin, the inhibition of malignant tumor growth and the induction of apoptosis. Retinoic acid [RA] is the active form of the retinol isoform of vitamin A, while retinol is its vitamer form found in food and is converted in the body to 11-trans-retinal by an oxidative process where the hydroxyl group is converted into an aldehyde. 11-trans-retinal is subsequently isomerized into 11-cis-retinal, the functional isomer of the vitamin important in the physiology of vision. Among carotenoids, beta carotene is the pro-vitamin A form obtained from vegetables. Hypervitaminosis A and the relative toxicity usually occur as a consequence of the administration of large amounts of vitamin A preparations, usually for therapeutic purposes. Many esters of vitamin A have been isolated and produced and following their topical use in cosmetics, allergic contact dermatitis has been reported. Furthermore, from retinoic acid, a new class of drugs largely used in dermatology have been produced and the first representant was the cis-retinoic acid or isotretinoin and many others which can be assumed orally to treat severe acne. Such drugs have induced contact dermatitis, photodermatitis, but also urticaria/angioedema with a pseudoallergic mechanism due to the imbalance of inflammatory prostaglandins. On the contrary, true allergic reactions like anaphylaxis from these vitamin A derivative drugs are attributed to their emulsifier, the soybean oil, able to induce severe reactions in peanut allergic patients.